diff --git a/bot.py b/bot.py
index efaa8b9..24ff95d 100755
--- a/bot.py
+++ b/bot.py
@@ -78,6 +78,7 @@ class BotClient(discord.Client):
                     calc = await self._calculate(args)
                     await message.reply(content=calc.strip())
                 except Exception as e:
+                    _log.exception("running calculation")
                     await message.reply(
                         content="```\n" + str(e) + "\n```", delete_after=30
                     )
diff --git a/calc.js b/calc.js
index 87332d2..0fc66d4 100644
--- a/calc.js
+++ b/calc.js
@@ -121,9 +121,7 @@ function* iterate(arr) {
 function unwrapToken(type, token) {
   assert(
     token.tokenType.name == type,
-    "expected token %s, got %s",
-    type,
-    token.tokenType.name
+    `expected token ${type}, got ${token.tokenType.name}`
   );
   return token.image;
 }